Producing high vacua



Patented June 19, 1934 1,963,829 PRODUCING HIGH VACUA Hugh S. Cooper, Cleveland, Ohio, assignor to Kemet Laboratories Company, Inc., a corporation of New York No Drawing. Application December 5, 1931, Serial No. 579,355

11 Claims. (Cl. 250-275) High vacua are customarily produced in thermionic tubes and the like by removing the greater part of the gas from the device by mechanical pumping, and cleaning up the residual traces of gas by the use of a clean-up agent or getter which, it is believed, fixesthe residual gases by both chemical and physical action. My invention relates to this process of producing high vacua, and although it is primar- LO ily directed to the production of vacua in thermionic valves and similar devices, it is applicable to the production of vacua generally. Clean-up agents are customarily placed within the device to be evacuated and later volatilized .15 by inductive electric heating; the volatilizing step being commonly termed flashing. The time and temperature required to ,flash the clean-up agent are frequently veryimportant factors in the manufacture of thermionic devices,

.20 especially when the manufacturing steps, which include flashing, are performed by automatic machinery, which is usually the case.

The objects of my invention are to provide a series of new clean-up agents characterized by the ease and rapidity with which they may be flashed, and to provide a method by which the time required to flash known clean-up agents may be reduced. I obtain these and other objects by taking advantage of the intense exo- .30 thermic reaction that results when aluminum alloys with nickel and cobalt.

According to my invention a clean-up agent is prepared by placing in mutual contact one of the following combinations: a metal predominantly of nickel, a metal predominantly of aluminum,

and a clean-up material; or a metal predominantly of nickel, and an aluminum alloy of a clean-up material; or a metal predominantly of aluminum, and a nickel alloy of a clean-up mate- 4,0 rial. Pure nickel and aluminum are generally preferable.

It is to be understood herein that cobalt is the substantial equivalent of nickel wherever the latter is used.

" The clean-up material used in the clean-up agent may be any metal or alloy thereof which is effective when volatilized within an envelope to fix residual traces of gas therein. For example, the alkaline earth metals and their alloys .50 such as barium, strontium, calcium, barium-sili; con alloy, and the like are suitable as a clean-up material.

According to one application of my invention, clean-up agents are prepared by closely associating metallic nickel with an aluminum alloy, either ductile or friable, containing a clean-up material such as an alkaline earth metal. One method of application is to flash while in mutual contact a piece of metal-comprising chiefly nickel and another piece of metal comprising the aluminum alloy or a plurality of lamina built up from alternate pieces of the two metals. The aluminum alloy may be in the form of ductile metal or a powdered friable alloy, and the latter may conveniently be compressed to a solid tablet. Another method of application, best suited to the friable aluminum alloys, is to flash an intimate mixture of powdered aluminum alloy and powdered nickel. This mixture may also be compacted into a tablet or the like if it is so desired.

. Another application of my invention consists in closely associating nickel and aluminum with a clean-up material such as an alkaline-earth metal or an alloy thereof, for example an alloy of barium and silicon. The nickel, aluminum and clean-up material may be powdered and intimately mixed, or closely associated in any similar suitable manner.

vA further application of my invention consists in associating aluminum with an alloy of nickel containing a clean-up material, for instance an alloy of nickel and barium. The aluminum and the alloy may both be solid ductile pieces, or both powdered, or either one powdered and the other a solid ductile piece. 7

The advantages of my invention are demonstrated by experiments which I have made. For example, I prepared a friable alloy comprising aluminum and barium in approximately equal proportions. A clean-up agent was prepared from this material, and introduced into a glass envelope, the envelope was mechanically-evacuated and the agent flashed. About 12 seconds flashing time was required. A portion of the same barium-aluminum alloy was then mixed in powdered form with about an equal weight of powdered nickel, a clean-up agent compressed and compacted therefrom, and the agent flashed under conditions substantially identical with those previously used. Only about 8 seconds flashing time was required for the alloy-nickel agent. The barium given off by the latter agent apparently is exceedingly pure, and the mirror formed by the agent upon the wall of the bulb was brighter and more silvery than is ordinarily secured when barium-containing agents are used. The barium-aluminum alloy per se is not a part of this invention.

In another experiment I prepared a bariumsilicon alloy containing about equal proportions 1 slightly more than 8' seconds.

Similarly, the time required to fiashan alloy of nickel and barium may be decreased by closely associating aluminum with the alloy.

When alkaline earth metal alloys of" aluminum or nickel are used, it is desirable to have at least 5% of the alkaline earth metal present" in the" alloy, so as to avoid the necessity of using an excessive amount of alloy to secure satisfactory clean-up of gases. 1,

Although I have described my invention" with' specific reference to the alkaline earth metalsas the clean-up materials, other clean-up materials may be used as substantial equivalents for the purpose. It is evident that the clean-up material may comprise any number of suitable metals inany proportions, and that they may be alloyed with either the nickel or the'aluminum', or be unalloyed with either. The nickel and the aluminum must not be alloyed with each other, that is to say, they must be physically separable.

I claim:

1. A clean-up agent suited forusein producingvacuawhich comprises-nickel, aluminum and a clean-up material, the nickel being alloyed with the clean-up material and the aluminum being physically separable from the said alloy.

-2. A clean-up agent suited for use in producing high vacua which comprises two metals in mutual contact, one metal being predominantly of aluminumand the other being an alloy of nickel withat least one c1eari-up material such as barium, strontium or calcium.

3 A clean-up agent suited for use in producing high vacua which comprises two metals in mutual, contact, one of said metals being substantially pure aluminum and the other being an alloy ofnickel with at leastone of themetals barium, strontium; calcium.

4. A clean-up agent suited for use inproduc-' ing high vacua which comprises aluminum and an alloy of nickel with at least 5% of barium;

the nickel and aluminum alloy being in mutual contact.

5. A clean-up agent suited for use in producing high vacua which comprises an intimate mixture of subdivided nickel, subdivided aluminum, and subdivided alloy of barium and silicon. 7 6. A olean-up agent suited for use in producing high vacua which comprises; an intimate mixture of powdered nickel and a powdered v;fr iable alloy of aluminum with at least one of the alkaline earth metals barium, strontium,

'7. A clean-up agent comprising an intimate mixture of powdered nickel and a powdered friable alloy comprising approximately equal parts of aluminum and barium.

8. Process" of producing a high vacuum which comprises introducing into an envelope. a cleanup agent consisting of nickel, aluminum and a clean-up material, the nickel and aluminum'beingphysically separable; mechanically evacuating said envelope; and alloying the nickel with the aluminum, thereby volatilizing at least par of the'clean-upf material in said agent; 7

9. Process of producing a high vacuum which comprises introducing into an envelope a clean-' upagent consisting of a metal predominantly of aluminum in contact with an alloy of nickel containing clean-up material; mechanically evacuating said envelope; and alloying the nickel with the aluminum, thereby volatilizing at least part of the clean-up material in said agent.

1'01 Process of producing ahigh vacuum which comprises introducing into an' envelope 3; cleanup. agentconsisting of two- .metals inmutual contact,- one beingcomposed predominantly of nickel and the other being an alloy of aluminum withatleast one of the group: barium; strontium and calcium; mechanically evacuating said envelo'pe; and: alloying the. nickel with the aluminum, thereby volatiiizingmat leastv part of the clean-up material-in said agent. I

11. A clean-up agent. suited for mom produci'ng vacua which comprises. a plurality of laminae; alternate laminae consisting-of a metal predominantly aluminum; and the remaining laminae consisting of an alloy comprising nickel and aclean-up material:-

HUGH s .cooPER. 

